System of distribution.



F. W. MEYER. SYSTEM OF DI$TR\BUTION. APPLICATION FiLED JAN. 11. 1913.

Patented Aug. 7 1917 \NVENTOR ATTORNEY UNITED PATENT FBIEDRICH'W. MEYER, OF WILKINSBURG, PENNSYLVANIA, vASSIGNOIB, 'TO WESTING- HOUSE ELECTRIC MANUFACTURING COMPANY A CORPORATION OF PENN- SYLVANIA.

SYSTEM 0F DISTRIBUTION.

PatentedAug. 7, 1917.

Original application filed October 7, 1911, Serial No. 853,380. Divided and this application filed January 11, .1913. SerialNo.741,458.

To all whomit may concern": 1

Be it known that I, llnnnnzron W. MEYER, a subject ofthe'Emperorof Germany, and-a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Systems of Distributionfof which the following is a specification, this application being a division of application Serial No. 653,380, filed October 7, 1911.

My invention relates to systems of electrical distribution and particularly to means for regulating the speed and powerfactor of an induction motor.

The object ofmy invention is to provide simple and economical means for regulating the speed of an induction :motor and causing it to operate ata good power factor under all conditions of load andspeed.

Because of simplicity of construction and economy in first costand in maintenance of induction motors, and also because of the simplicity of the supply system, it is highly desirable to employ such motors for the operation of hoists, rolling mills, and similar apparatus, and considerable attention has accordingly been devoted'to the problem of'obtaining a large range of economical speed regulation of the motors. To this end, it has heretofore been proposed to employ an auxiliary commutatormachine as a means for regulating the speed of the motor, and of obtaining a certain degree of power factor compensation, the auxiliary machine serving either to assist the induction :motor in -carrying the load,- orto return the energy .of its secondary circuitor rotor .tothe supply circuit. However, in such "previous arrangements, either the auxiliary machine must be large, especially if the motor speed islow and a large range of speed regulation is'desired, or a second auxiliary machine is necessary. Furthermorain previous systems, it is impossible to adjust the vpower factor of the induction motor to suit varying operating conditions, except by :the provision of expensive and complicated auxiliary Windings or combinations of windings, or by shifting the brushes of the auxiliary machine, which iii-objectionable since it inter feres with good commutation.

According to the present invention, only a single small auxilia machine is employed, and the power actor and speed of the induction motor may be readily and separately adjusted without shiftingthe brushes of 'the'auxiliary machine or otherwise detrimentally affecting its commutation.

My invention is'illustrated in the accompanying drawings, Figure 1 of which is a diagrammatic view of a system of distribution embodying the same, and Figs. 2 and 3 are similar views of modifications of the system of Fig. 1.

In each of the systems illustrated, an induction motor 1, that is adapted todrivetany suitable load (not shown), such as a compressor, hoist or rolling mill,has its primary winding connected to, and receives energy from, a suitable supplycircuit 2. The secondary winding of the induction motor is connected through-slip rings3 to the armature 4 of an auxiliary machine or frequency changer 5, the said armaturebeing provided with 'both a commutator 6 and slip rings 7 and being alsoconnccted, either-directly or indirectly, to the supply circuitQ. The "energy of the secondary circuitor rotor of :the

induction motor thus passes through "the auxiliary regulating machine or frequency changer,and is returned to the supply circuit.

In the system of Fig. '1, thecommutator 6 of the auxiliary machine is connected to the slip rings 3 of the induction Vmotor 1, and the slip rings 7 of the auxiliary machine are connected to suitable points in one of the windings of a transformer 8, the other winding of which is connectedto the supply circuit. The transformer 8 serves both as means for transforming the voltage .of'the current received from the vslip rings 7 of the auxiliary machine to a "voltage suitable for application to the supply circuit, and as means for regulating the speeds of the induction motor and auxiliary machine.

The auxiliary machine 5 is provided with a simple three-phase field or stator winding 10 that is connected in closed circuit relation with variableresistances 11, but is other- Wise entirely unconnected with other circuits of the system. The currents 'in the field or stator winding are only such asare induced therein and are only suiiicient to give the torque required to overcome the v riction of the :machine and to cause it to run at the proper speed. This is because the field produced by the current flowing through the commutatoris counteracted by the current flowing to the frequency changer through the slip rings, with the exception of that necessary field.

In the operation of the system, the induction motor 1 is started in any usual manner,

and the auxiliary machine is also started by supplying it from the supply circuit through the regulating transformer 8 with current at a voltage corresponding to the desired voltage on the rotor of the induction motor, and the current in the stator winding 10 is then regulated by means of resistances 11 until the auxiliary machine runs in synchronism relatively to the induction motor. At this time, the connections between the slip rings of the induction motor and the commutator of the auxiliary machine are established, as shown, so that the energy in the secondary circuit or rotor of the induction motor may flow through the auxiliary machine and the regulating transformer to the supply circuit. Other methods may, of course, be employed, if desired, for starting the machines and bringing them into relative synchronism. The machines will thereafter continue to operate in relative synchronism under all working conditions, because of the synchronizing power of the frequency changer, and the speed of the induction motor may then be regulated by adjustment of'the regulating transformer 8'so as to vary the voltage upon the secondary winding or rotor of the induction motor.

If, when the two machines are operating in relative synchronism, the resistances 11 are adjusted without changing the regulating transformer 8, the auxiliary machine or frequency changer has a tendency to correspondingly change its speed, which,- however, is prevented on accountof its connection to the induction motor and the synchronizing power of the auxiliary machine. The result is that equalizing currents will flow between the rotors of the two machines, which currents are lar ely wattless and produce a synchronizing orce. The current in the regulating transformer 8 hasa large wattless component which produces the field of the auxiliary machine, and also that of the induction motor. However, by regulating the resistances 11, and thereby the currents in the stator winding of theauxiliary machine, a greater wattless comfponent may be produced than is necessary or the production of these fields, with the result that the main motor current may be made to lead to such an extent that theresulting current of the Whole system will have substantially the same hase as the voltage or any other desired rdlation to it. The auxiliary machine serves only as a frequency changer, and the regulation of the current in its field or stator winding serves primarily to regufor magnetizing the working late only the power factor of the induction motor, though such power factor regulation is necessarily accompanied by a small degree of speed regulation, because the voltage rop in the machines varies somewhat when the wattless current is changed. When the power factor is improved, the speed in creases, and vice versa. Consequently, if variations in power factor are permissible, very fine speed regulation may be obtained by adjustment of the resistances 11.

The use of the regulating transformer, as shown in Fig. 1, may be avoided in lowvoltage systems by providing the auxiliary machine or frequency changer 13 with a stator or field winding having its several phase portions 14, 15 and 16 connected in star relation, as shown in Fig. 2. The stator Winding is included in the connections between the slip rings 3 of the induction motor and the commutator of the auxiliary machine or frequency changer, the several connections to the said stator winding being adjustable so that the said winding may serve the function of a voltage regulator of the auto transformer type, in addition to its ordinary function. The voltage of the secondary winding or rotor of the induction motor, and

consequently the speed of the motor, may be regulated, by changing the ratio of the lengths of the several divisions of the field.

winding between the neutral or common connection thereof and the nection thereto of the secon ary slip rings of the induction motor, to the lengths of the said portions of the windings between the neutral or common connection thereof and the points of connection thereto of the commutator brushes of th auxiliary machine.

However, if this ratio is maintained unioints of con ice 1? form, which is equivalent to maintaining the ratio of transformation uniform in the transformer 8 of Fig. 1, while the points of connection to the several phase divisions of the stator winding are adjusted, so as to chan e the actual number of active turns in the said divisions of the stator winding and thereby vary the strength of the field, the wattless or equalizing currents will change and effect an adjustment of the power factor of the induction motor, as in the system-of Fi 1.

When it is necessary or desirabfe to operate the induction motor at or near synchronous speed, the system of Fig. 3 may be preferable to that of Fig. 2, as finer steps of speed regulation may be obtained at or near synchronous speed, because of greater uniformity of the field, although the auxiliary machine or the frequency changer is In this system,

thereto upon either side of their common point of connection to permit of convenient operation of the set either above or below synchronism. In this case, the sli rings of theinduction motor are connects to the slip rings of the auxiliary machine or freuency changer and the stator winding of t e frequency changer is included in the connections between the commutator brushes and the supply circuit. In this system, the induction motor may be run above synchronism and the auxiliary machine correspondingly below synchronism, by interchanging one pair of the connections between the machines.

I claim as my invention:

1. A system of distribution comprising a supply circuit, an induction motor supplied therefrom, an auxiliary machine having a stator winding, and an armature provided with a commutator and a set of slip rings that are connected respectively to the secondary winding of the induction motor and to the supply circuit, and resistances connected in closed circuit with the stator winding of the auxiliary machine.

2. A system of distribution comprising a supply circuit, an induction motor supplied therefrom, an auxiliary machine operated by its own motoric forces relatively in synchronism with the induction motor and having an armature provided with a commutator and a set of slip rings, one of which is connected to the supply circuit, and the other to the secondary windin of the induction motor, a stator winding for the auxiliary machine electrically disconnected from the remaining portions of the system, and means for adjusting the current in said stator winding.

3. A system of distribution comprising a supply circuit, an induction motor supplied therefrom, an auxiliary machine operated by its own motoric forces relatively in synchronism with the induction motor and having an armature provided with a commutator and a set of slip rings, one of which is connected to the supply circuit, and the other to the secondary winding of the induction motor, a stator winding for the auxiliary machine electrically disconnected from the remaining portions of the system, and adjustable resistance members connected in closed circuit relation with said stator winding for controlling the current flow therein.

In testimony whereof, I have hereunto subscribed my name this 31st day of December 1912.

FRIEDRICH w. MEYER. 

